sleep

Hi, I'm using:

  # sleep --version
sleep (GNU sh-utils) 2.0
Written by FIXME: unknown.

Copyright (C) 1999 Free Software Foundation, Inc.

The manual states:
"Historical implementations of `sleep' have required that NUMBER be
an integer.  However, GNU `sleep' accepts arbitrary floating point
numbers."

I tried with

sleep 0.5
sleep 0,5
sleep 0.5s
sleep 0,5s
sleep 0.5d
sleep 0,5d


... but I always get

sleep: invalid time interval

So, *if* I can specify arbitrary floating point numbers, how do I do that?
And what happened to the good old tradition of putting examples in the 
man, something that often saves pages of text? (well, that's a general 
and broad *sigh*, nothing you should feel an obligation to answer.)

regards, JO